Quantum Liquid States of Spin Solitons in a Ferroelectric Spin-Peierls State.

In this study, we performed high-magnetic-field magnetization, dielectric, and ultrasound measurements on an organic salt showing a ferroelectric spin-Peierls (FSP) state, which is in close proximity to a quantum critical point. In contrast to the sparsely distributed gaslike spin solitons typically observed in conventional spin-Peierls (SP) states, the FSP state exhibits dense liquidlike spin solitons resulting from strong quantum fluctuations, even at low fields. Nevertheless, akin to conventional SP systems, a magnetic-field-induced transition is observed in the FSP state. In conventional high-field SP states, an emergent wave vector results in the formation of a spin-soliton lattice. However, in the present high-field FSP state, the strong quantum fluctuations preclude the formation of such a soliton lattice, causing the dense solitons to remain in a quantum-mechanically melted state. This observation implies the realization of a quantum liquid-liquid transition of topological particles carrying spin and charge in a ferroelectric insulator.

Extremely high upper critical field in BiCh2-based (Ch: S and Se) layered superconductor LaO0.5F0.5BiS2-xSex (x = 0.22 and 0.69).

Centrosymmetric compounds with local inversion symmetry breaking have tremendously interesting and intriguing physical properties. In this study, we focus on a BiCh2-based (Ch: S, Se) layered superconductor, as a system with local inversion asymmetry, because spin polarisation based on the Rashba-Dresselhaus-type spin-orbit coupling has been observed in centrosymmetric BiCh2-based LaOBiS2 systems, while the BiCh2 layer lacks local inversion symmetry. Herein, we report the existence of extremely high in-plane upper critical fields in the BiCh2-based system LaO0.5F0.5BiS2-xSex (x = 0.22 and 0.69). The superconducting states are not completely suppressed by the applied magnetic fields with strengths up to 55 T. Thus, we consider that the in-plane upper critical field is enhanced by the local inversion symmetry breaking and its layered structure. Our study will open a new pathway for the discovery of superconductors that exhibit a high upper critical field by focusing on the local inversion symmetry breaking.

Above-ordering-temperature large anomalous Hall effect in a triangular-lattice magnetic semiconductor.

While anomalous Hall effect (AHE) has been extensively studied in the past, efforts for realizing large Hall response have been mainly limited within intrinsic mechanism. Lately, however, a theory of extrinsic mechanism has predicted that magnetic scattering by spin cluster can induce large AHE even above magnetic ordering temperature, particularly in magnetic semiconductors with low carrier density, strong exchange coupling, and finite spin chirality. Here, we find out a new magnetic semiconductor EuAs, where Eu2+ ions with large magnetic moments form distorted triangular lattice. In addition to colossal magnetoresistance, EuAs exhibits large AHE with an anomalous Hall angle of 0.13 at temperatures far above antiferromagnetic ordering. As also demonstrated by model calculations, observed AHE can be explained by the spin cluster scattering in a hopping regime. Our findings shed light on magnetic semiconductors hosting topological spin textures, developing a field targeting diluted carriers strongly coupled to noncoplanar spin structures.

Three-dimensional Winston-Lutz test using reusable polyvinyl alcohol-iodide (PVA-I) radiochromic gel dosimeter.

Medical linear-accelerator-based stereotactic radiosurgery (SRS) using a stereotactic apparatus or image-guided radiotherapy system for intracranial lesions is performed widely in clinical practice. In general, Winston-Lutz (WL) tests using films or electric portal imaging devices (EPIDs) have been performed as pre-treatment and routine quality assurance (QA) for the abovementioned treatment. Two-dimensional displacements between the radiation isocentre and mechanical isocentre are analysed from the test; therefore, it is difficult to identify the three-dimensional (3D) isocentre position intuitively. In this study, we developed an innovative 3D WL test for SRS-QA using a novel radiochromic gel dosimeter based on a polyvinyl alcohol-iodide (PVA-I) complex that can be reused after annealing. A WL gel phantom that was consisted of the PVA-I gel dosimeter poured into a tall acrylic container and an embedded small tungsten sphere was used as a position detector. A flatbed scanner was used to analyse the isocentre position. The measured 3D isocentre accuracy from the gel-based WL test was within 0.1 mm compared with that obtained from the EPID-based WL test. Furthermore, excellent reusability of the WL gel phantom was observed in long-term SRS isocentre verification, in which clinical SRS cases involving repeated irradiation and annealing were analysed. These results demonstrate the high accuracy and reliable evaluation of the isocentre position using an innovative test. In addition, the clinical-based routine SRS-QA using the PVA-I gel dosimeter demonstrates a highly convenience while affording an easy and fast analysis process.

Giant anomalous Hall effect from spin-chirality scattering in a chiral magnet.

The electrical Hall effect can be significantly enhanced through the interplay of the conduction electrons with magnetism, which is known as the anomalous Hall effect (AHE). Whereas the mechanism related to band topology has been intensively studied towards energy efficient electronics, those related to electron scattering have received limited attention. Here we report the observation of giant AHE of electron-scattering origin in a chiral magnet MnGe thin film. The Hall conductivity and Hall angle, respectively, reach [Formula: see text] Ω-1 cm-1 and [Formula: see text]% in the ferromagnetic region, exceeding the conventional limits of AHE of intrinsic and extrinsic origins, respectively. A possible origin of the large AHE is attributed to a new type of skew-scattering via thermally excited spin-clusters with scalar spin chirality, which is corroborated by the temperature-magnetic-field profile of the AHE being sensitive to the film-thickness or magneto-crystalline anisotropy. Our results may open up a new platform to explore giant AHE responses in various systems, including frustrated magnets and thin-film heterostructures.

Anisotropic Quantum Transport through a Single Spin Channel in the Magnetic Semiconductor EuTiO3.

Magnetic semiconductors are a vital component in the understanding of quantum transport phenomena. To explore such delicate, yet fundamentally important, effects, it is crucial to maintain a high carrier mobility in the presence of magnetic moments. In practice, however, magnetization often diminishes the carrier mobility. Here, it is shown that EuTiO3 is a rare example of a magnetic semiconductor that can be desirably grown using the molecular beam epitaxy to possess a high carrier mobility exceeding 3000 cm2 V-1 s-1 at 2 K, while intrinsically hosting a large magnetization value, 7 µB per formula unit. This is demonstrated by measuring the Shubnikov-de Haas (SdH) oscillations in the ferromagnetic state of EuTiO3 films with various carrier densities. Using first-principles calculations, it is shown that the observed SdH oscillations originate genuinely from Ti 3d-t2g states which are fully spin-polarized due to their energetical proximity to the in-gap Eu 4f bands. Such an exchange coupling is further shown to have a profound effect on the effective mass and fermiology of the Ti 3d-t2g electrons, manifested by a directional anisotropy in the SdH oscillations. These findings suggest that EuTiO3 film is an ideal magnetic semiconductor, offering a fertile field to explore quantum phenomena suitable for spintronic applications.

Quantized surface transport in topological Dirac semimetal films.

Unconventional surface states protected by non-trivial bulk orders are sources of various exotic quantum transport in topological materials. One prominent example is the unique magnetic orbit, so-called Weyl orbit, in topological semimetals where two spatially separated surface Fermi-arcs are interconnected across the bulk. The recent observation of quantum Hall states in Dirac semimetal Cd3As2 bulks have drawn attention to the novel quantization phenomena possibly evolving from the Weyl orbit. Here we report surface quantum oscillation and its evolution into quantum Hall states in Cd3As2 thin film samples, where bulk dimensionality, Fermi energy, and band topology are systematically controlled. We reveal essential involvement of bulk states in the quantized surface transport and the resultant quantum Hall degeneracy depending on the bulk occupation. Our demonstration of surface transport controlled in film samples also paves a way for engineering Fermi-arc-mediated transport in topological semimetals.

Efficient delivery of siRNA using dendritic poly(L-lysine) for loss-of-function analysis.

RNA interference (RNAi) is a valuable tool for the validation of gene identification and functional genomics. Previously, it was reported that 6th generation dendritic poly(L-lysine) (KG6) transfected DNA into several cultivated cell lines with high efficiency and without any cytotoxic effects. In this study, the potential of KG6 to be an efficient siRNA carrier is investigated. KG6 showed effective knockdown of GAPDH with low cytotoxicity in combination with the weak-base amphiphilic peptide, Endo-Porter. In addition, the knockdown of PEPCK, which is the rate-limiting enzyme for gluconeogenesis, led to a reduction in glucose production in rat hepatoma H4IIEC3 cells. Knockdown of organic cation transporter 1 (OCT1), which is thought to be the gene that influences metformin action, was shown to successfully diminish the ability of metformin to inhibit gluconeogenesis in H4IIEC3 cells. In conclusion, using a combination of KG6 and Endo-Porter, a model system in which genes that influence metformin action can be identified was successfully constructed.